1. Field of the Invention
The present invention relates to a vision measuring device which measures a measuring target contactlessly based on images acquired by imaging the measuring target, and an auto-focusing control method.
2. Description of the Related Art
Vision measuring devices are required to be highly accurate as compared with digital cameras for general consumers, depending on the purposes, to be good at throughput. To satisfy such requirements and perform quick and highly-accurate measurement, a three-dimensional vision measuring device having an auto-focusing function is disclosed in JP2001-319219A.
In contrast-type auto-focusing, imaging is performed by gradually changing the in-focus position of an imaging device such as a camera, and the in-focus position is determined based on the contrast of the acquired images. Such a method can be realized by a simple configuration including, for example, only a camera and software. However, depending on the communication system for connecting the camera and the software, an indeterminate delay or drop frame might occur while images are being transferred due to communication confliction, etc., or a fixed gap might occur between the position at which image shooting is performed and the position at which a resulting image is acquired because the imaging device performs imaging while it is moving. Hence, it becomes impossible to determine the actual position at which the image is acquired, and hence to obtain the correct in-focus position. Moreover, this gap is different from device to device because of their own individual characteristics, and such handlings as individual calibration is needed because the gap directly becomes a measurement error.